There exist numerous machines having moving parts which can be dangerous for the person now working with the machines. Among such machines are for example presses, extruders, molding machines, grinders, which all have movable members adapted to cause accidents if people using these machines have the possibility to enter danger zones of these machines.
To avoid accidents, it has been proposed to provide protector elements, grills, panels or other members, displaceable from an inactive position in which access to the machine is permitted, to an active position in which certain zones of the machine are no longer accessible. An automatic device ensures that the supply of energy to the machine be interrupted as soon as the protector element is no longer active.
Such protector devices for machines are for example described in EP 0 363 810; GB 1 534 606; GB 2 084 279; GB 2 132 933 and U.S. Pat. No. 3,902,582.
In certain types of machines, for example granulators, the danger zone of the machine must be observed during observation of the latter, the protector elements must be transparent, or provided with grills. But during their operation, these machines throw particles against the protector elements, rendering them opaque. To clean these protector elements, it is necessary, with existing machines, to stop the machine and then to restart it only when the cleaned protector element is in place.
This leads to frequent stopping and substantial down time of the machine whose productivity is considerably lowered.